高磷饮食对慢性肾衰竭大鼠肾脏Ⅱa型Na-Pi转运体的影响

Effect of High-phosphate Diet on Type Ⅱa Sodium-dependent Phosphate Cotransporter mRNA Expression in the Kidney of Rat with Chronic Renal Failure

目的:研究高磷饮食对慢性肾衰竭(CRF)大鼠肾脏Ⅱa型钠-磷协同转运体(NaPi鄄2)mRNA表达的影响。方法:24只SD大鼠,随机分为CRF高磷饮食组、CRF低磷饮食组、假手术高磷饮食组与假手术低磷饮食组,用5/6肾大部切除术构建CRF大鼠模型,分别予高磷(含磷1.2%)或低磷(含磷0.2%)饮食,测定2、7、14天血离子钙(iCa)、磷(P)、全段甲状旁腺激素(iPTH);第14天测血1,25鄄(OH)2D3,RT鄄PCR法检测NaPi鄄2mRNA表达。结果:2周后CRF模型中高磷饮食组较低磷组肾脏NaPi鄄2mRNA表达明显减低(P<0.01),血P明显增高(P<0.05),iPTH明显增高(P<0.01),血iCa及1,25鄄(OH)2D3两组无明显差异(P>0.05)。假手术组中高磷饮食组较低磷组NaPi鄄2mRNA表达减低(P<0.05),血iCa、P、iPTH及1,25鄄(OH)2D3均无变化(P>0.05)。CRF组较假手术组NaPi鄄2mRNA表达明显减少(P<0.05)。结论:高磷饮食引起CRF大鼠NaPi鄄2mRNA表达减少,高磷血症可能是iPTH增高、不受钙和1,25鄄(OH)2D3影响的独立因素。

Objective: To investigate the effect of high-phosphate(Pi) diet on type Ⅱa cotransporter(NaPi-2) mRNA expression in the kidney of rats with chronic renal failure. Methods: Twenty-four male Sprague-Dawley rats underwent 5/6 nephrectomy or sham operation. The animals were randomly divided into two dietary groups: high-Pi diet(1.2% P) and low-Pi diet(0.2% P). Serum ionized calcium(iCa), phosphate,1,25-(OH)2D3 and intact parathyroid hormone(iPTH) level were detected at day 2,7,14. Semi-quantitative reverse transcription polymerase chain reaction(RT-PCR) was applied to detect NaPi-2 after two weeks. Results: In CRF rats, after two weeks, the expression of NaPi-2 mRNA was significantly decreased in high-Pi diet than low-Pi diet(P < 0.01). Meanwhile, serum P and iPTH level were significantly higher in high-Pi diet group than in low-Pi diet(P < 0.05 and P < 0.01 respectively). There was no significant difference in serum iCa and 1,25-(OH)2D3(P > 0.05). In sham-operated rats, the expression of NaPi-2 mRNA was decreased in high-Pi diet than in low-Pi diet(P < 0.05), but there was no significant difference in serum P, iCa,1,25-(OH)2D3 and iPTH(P > 0.05). The expression of NaPi-2 mRNA was decreased in CRF rats than in sham-operated rats(P < 0.05). Conclusion: High-Pi diet can decrease NaPi-2 mRNA expression in the kidney of CRF rats. Hyperphosphatemia is maybe a factor to stimulate the increase of iPTH independence of iCa and 1,25(OH)2D3.